// 后台任务的返回值
#include <future>
#include <iostream>

int find_the_answer_to_ltuae();
void do_other_stuff();

int main()
{
    std::future<int> the_answer = std::async(find_the_answer_to_ltuae);
    do_other_stuff();
    std::cout << "the answer is " << the_answer.get() << std::endl;
}